The present invention relates to an apparatus for cutting off a thickness of wood or veneer from logs.
In cutting a log with a rotary veneer lathe or a slicer having a tangential knife to form veneer sheets, cracks are often observed to form ahead of the cutting edge of the knife. Due to the presence of such cracks, proper advance of the cutting edge through the log is prevented. As a result, the surfaces of the cut-off sheets are quite rough, and they are not of uniform thickness. In manufacturing plywood using these sheets as veneer, this phenomenon leads to degradation of the surface quality of the plywood. To solve this problem, a conventional type of veneer lathe or slicer employs a unitary pressing member such as a pressure bar. In cutting a rotating log, for example, this pressure bar is pressed against the peripheral surface of the log slightly ahead of the cutting edge of the tangential knife over the axial length of the log.
Usually, however, the log has a number of knars scattered therein. These knars are hard and fragile, and not as elastic as the rest of the log. Therefore, if the pressure bar pressing the log with an ordinary force encounters a knar, the knar resists and prevents the rest of the log from being pressed effectively. If, however, the pressing force of the bar is increased in order to press the rest of the log effectively, the resisting knar often reaches its breaking point, causing holes or cracks to form in the produced veneer sheets. This drawback is due to the fact that the log is pressed throughout its axial length by a unitary pressure bar.
In addition, a crude log, before it is cut, is not exactly cylindrical in shape because of the irregularities on its peripheral surface. On the other hand, the portion at which the pressure bar makes contact with the log's surface is straight and smooth. Therefore, the pressure bar does not always make contact with the log's surface while the knife cuts the log throughout its axial length. As a result, the pressure bar does not serve its intended purpose until the cutting provides the log with an exact cylindrical shape.